Mo-99 isotope production calculation in the ICMSR (Innovative Compact Molten Salt Reactor) with the computer code MCNP6 has been carried out. ICMSR is a conceptual design of the MSR type reactor that uses NaF-ThF4-UF4 fuel with an enrichment of 235U of 19.75%. This reactor operates in thermal neutron spectrum with a graphite moderator. ICMSR is a power reactor that produces Mo-99 as a by-product. Calculations carried out for 12 days of operation show that the reactor condition is still critical so that there will be no intervention from refueling. The total Mo-99 produced until the 12th day is 9.118 x 106 Ci. Mo-99 can be extracted from the reactor as long as the power reactor is operating so it will be economically advantageous.Keywords: 99Mo, isotope production, ICMSR, MCNP, criticality